1. Field of the Invention
The invention relates to a composition and method for protecting pipeline joints. More particularly, the invention relates to a composition and a method for infilling the space at a welded joint in a coated (ex. concrete, polyethylene, etc.) pipeline between the ends of the coating on sequential joints of pipe.
2. Description of the Related Art
Offshore pipelines larger than about 12 inches in diameter are commonly coated with a thick layer of concrete to weight the pipeline down in the water. Such concrete coatings or weight coatings are applied to individual lengths of the pipe with the coating extending the full length of the pipe except for several inches near each end. Prior to applying the concrete coating, the pipe lengths are usually coated with a material, such as epoxy, to protect the pipe from corrosion. This coating material is also terminated several inches from each end. Successive lengths of pipe are joined together by welding, leaving a gap in the coating material and in the concrete covering at each joint.
It is the usual practice to apply a coating to the pipe in this gap to protect the pipe against corrosion, for example with a hot fusion bonded epoxy and/or a shrink sleeve, and to fill the gap between the ends of the concrete coatings so as to provide a smooth, uninterrupted covering for the pipeline. The pipeline can then move smoothly over the pipeline lay barge or vessel rollers and down the stinger to the sea bed.
The gaps in the pipeline have been filled with various materials by various techniques. One procedure that has been used is to place a metal sleeve or mold over the gap and fill the sleeve with molten mastic which solidifies as it cools. However, in most cases the pipeline must be in a condition for handling immediately after the gaps are filled, so that the laying of the pipeline can proceed without delays. The mastic filling does not set to a sufficiently strong material within the required time to allow further processing of the pipe without additional reinforcement to protect the mastic. Therefore, in conventional filling operations where mastic is used, the sleeve is left in place, so that it remains on the pipe on the ocean floor. This is objectionable, since the sleeve can snag fishnets, and cause other damage to marine operations. Moreover, the filling of the gaps with mastic in this way is highly labor intensive, and therefore expensive.
Another method that has been used to fill the gaps in concrete coated pipeline joints utilizes a fast cure material inside a removable mold which is removed before the pipe is advanced into the water. Various polymer concretes, such as those disclosed in U.S. Pat. No. 4,608,280, or polyurethanes have been used in this way. The removable mold surface is coated with a release agent to prevent the fast cure material from sticking to the mold surface. Such a mold release adds expense and processing time, and is inefficient if improperly applied. Furthermore, some of the release material remains on the surface of the fast cure material and enters the water with the pipe as a potential environmental contaminant.
Other techniques replaced the mastic filler with other types of materials. In the methods disclosed in U.S. Pat. Nos. 5,328,648 and 5,489,405, the exposed portion of pipe was covered with a mold which was then filled with a filler material. The filler materials included granular or particulate matter having between about 1/16 inch to 1 inch diameter such as gravel, iron ore, wood chips, etc. which would not pack solidly or uniformly. Elastomeric polymers were then injected into the mold in an attempt to fill the interstices between the granular fill materials. The preferred polymers included rapid setting solid polyurethanes, as for example those prepared by the reaction of the polyhydroxyl containing compounds and the organic polyisocyanates described in U.S. Pat. Nos. 3,983,064, 4,154,716, and 4,246,363. After the polymer components had reacted completely the mold would be removed from the surface of the infill. The elastomeric polymers used in this method included a liquid modifer consisting primarily of aromatic hydrocarbons. The use of aromatic hydrocarbons in this application has several disadvantages including air and marine environmental and safety issues.
Another technique, disclosed in U.S. Pat. No. 4,909,669, involved wrapping the exposed portions of pipe with a thermoplastic sheet. The sheet overlapped the ends of the weight coat adjacent the exposed joint and was then secured in place by screws, rivets, or straps. To increase the rigidity and impact resistance this joint protection system required the installation of reinforcing members such as plastic bars or tubes to the interior of the sheet. The reinforcement bars or tubes either had to be precut and stored on the barge or else cut to the required fitting form as part of the installation process on the barge. This required additional handling and made the installation process more difficult.
Another method of reinforcing this joint protection system was to fill the lower portion of the annular space between the pipe and the plastic sheet with a material such as pre-formed foam half shell. When foam half shells were used in the lower portion of the annular space to provide support, the upper portion of the joint and the corrosion coating was in effect protected only by the plastic sheet enclosing the upper portion which had no foam covering. This could cause a particular problem if the pipelines were located where they would encounter the drag lines or trawler boards attached to the nets of fishing trawlers. The corrosion coating on the upper portion of the pipe joint could become damaged by this type of towed object. An additional problem with this joint protection system occurred when pipelines were laid in shallow waters, i.e., less than about 200 feet deep. Pipelines in shallow waters were often buried by using high pressure water jets which were directed at the ocean floor where the pipelines were to be buried. The water jets would wash out a trench into which the pipelines would be dropped for burial. The joint protection system could be damaged when the water jets came in contact with the pipeline joint because the plastic sheet over the top of the pipe joint was not reinforced.
Another method for protecting exposed pipeline joint sections, disclosed in U.S. Pat. Nos. 5,900,195 and 6,402,201, begins by forming a pliable sheet of cover material into a cylinder which is fitted over the exposed portions of the joint connection. The longitudinal end portions of the pliable sheet of cover material overlap the adjacent edges of the weight coating. Side edge portions of the sheet of cover material forming the cylinder are then overlapped tightly such that an annular pocket is formed about the exposed joint section. The outside side edge is then sealed to the surface of the sheet of cover material, completely encasing the exposed pipe and the annular pocket or space. Polyurethane chemicals are then injected into the empty annular space where they react to form a high density foam which fills the annular space. The cover material remains part of the joint fill and is not removed.